Randy Chandler
Enzymes are essential in the process of transforming liquid milk into solid cheese. The most commonly used enzyme is rennet, which is produced in the stomachs of ruminant mammals. Rennet contains two enzymes: chymosin, which causes milk to coagulate into curds, and pepsin, which impacts the aging process of cheese. While traditional rennet is derived from calf stomachs, alternative sources of enzymes for cheese production include plants, fungi, and microbial sources. These substitutes are suitable for vegetarians and those keeping kosher or halal diets.
| Characteristics | Values |
|---|---|
| Purpose | To trigger coagulation and transform liquid milk into a solid coagulum or curd |
| Sources | Animal (kid, calf), vegetable (thistle, Cynara, artichokes, cardoons, fig juice, dried caper leaves, nettles, mallow, Withania coagulans, ground ivy), microbial, fungal |
| Composition | Chymosin, pepsin, lipase |
| Type | Coagulant |
| Use | Used in small quantities, acts on proteins in milk |
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What You'll Learn
Rennet: a complex set of enzymes produced in the stomachs of ruminant mammals
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. It is a crucial ingredient in cheesemaking, used to coagulate milk and form curds, which are then transformed into cheese. The process involves the clumping of proteins, trapping fat and other solids, resulting in a solid coagulum or curd.
Rennet's key component is chymosin, a protease enzyme that curdles casein, the primary protein in milk. This curdling action is essential for cheese production. In addition to chymosin, rennet contains other enzymes like pepsin and lipase. The combination of these enzymes gives rennet its unique properties.
Calf rennet, derived from calves' stomachs, is a traditional and natural source of rennet. It contains chymosin and pepsin in a natural ratio, influencing both the yield and flavour profile of the cheese. Calf rennet has been preferred for its reliable results and flavour, contributing to less defective cheese. However, due to limited availability and ethical considerations, cheese makers have explored alternative sources of rennet.
Today, most cheese is produced using chymosin derived from bacterial sources. Fermentation-produced chymosin (FPC) is widely used in industrial cheesemaking in North America and Europe due to its cost-effectiveness. This chymosin is often obtained through genetic engineering, introducing rennet genes into bacteria, fungi, or yeasts. While FPC does not contain any animal-based ingredients, its presence in cheese may be a concern for those adhering to strict vegetarian or vegan diets.
The use of rennet in cheesemaking dates back to ancient times, with various cultures employing different sources. For example, Mediterranean cheese producers have traditionally used enzymes from thistle or Cynara (artichokes and cardoons), while Homer's Iliad suggests that the ancient Greeks used fig juice for coagulation. Other natural sources of enzymes include various plants, fungi, and microbial sources, making cheese production accessible to those with dietary restrictions and religious practices.
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Chymosin: a protease enzyme that curdles the casein in milk
Milk is an emulsion of fat, protein, sugar, and minerals suspended in water. To transform liquid milk into a solid coagulum, or curd, cheesemakers use enzymes to trigger a chemical reaction that causes coagulation. Rennet is the general name for enzymes that act on proteins in milk. Rennet contains two enzymes: chymosin and pepsin.
Chymosin, a protease enzyme, is the key component of rennet. It curdles the casein in milk, causing coagulation. Casein is the main protein in milk. Cleaving the kappa casein chain, chymosin removes the slightly negatively charged glycomacropeptide (GMP) from the surface of the casein micelle. As negative charges repel each other, the GMP prevents casein micelles from adhering to each other.
Chymosin is traditionally derived from the stomachs of ruminant mammals, such as calves, goats, and cows. However, due to the limited availability of mammalian stomachs, cheesemakers have sought alternative sources of chymosin. Fermentation-produced chymosin (FPC) is now commonly used in industrial cheesemaking in North America and Europe. This type of chymosin is produced by introducing rennet genes from animals into certain bacteria, fungi, or yeasts. The genetically modified microorganism is then killed after fermentation, and the chymosin is isolated from the fermentation broth. Over 80% of cheese consumed in North America is made using non-animal sources of chymosin.
In addition to animal and fermentation-produced chymosin, plant sources of chymosin have also been used in cheesemaking. For example, in India, fruit trees are used as a source of chymosin, while Spanish sheep's milk cheeses often use thistle and cardoon rennet. However, plant-based coagulants may lead to bitter and undesirable flavors in cow's milk cheeses.
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Pepsin: impacts the aging process of cheese
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. It is a key ingredient in cheesemaking, with calf rennet being a traditional variant. Calf rennet contains two enzymes, chymosin and pepsin, in a natural ratio that suits specific types of cheese. Chymosin is responsible for coagulation, while pepsin influences the aging process.
Pepsin's impact on the aging process is significant, as it contributes to the development of the cheese's flavour, texture, and aroma. Aging, or ripening, transforms fresh curds into complex, flavourful cheeses. During aging, cheese undergoes a series of chemical and biological changes, influenced by factors such as humidity, temperature, and airflow. These factors are carefully controlled by cheesemakers to achieve the desired characteristics in the final product.
The aging process introduces nutty, fruity, or pungent notes to the cheese. The length of aging directly affects the flavour intensity. For example, a young cheddar has a mild, tangy taste, while an aged cheddar develops sharp, complex flavours with nutty hints. Aging also affects the texture of the cheese. Fresh cheeses like mozzarella are soft and moist, while aged, hard cheeses like cheddar or Parmesan lose moisture, becoming firmer and sometimes crumbly. Some aged cheeses even develop protein crystals, creating a crunchy texture.
Pepsin plays a crucial role in achieving these desired characteristics during the aging process. However, the use of pepsin in cheese production has some considerations. Calf rennet, which contains pepsin, is derived from the inner mucosa of the fourth stomach chamber of young calves, which is a byproduct of veal production. This raises ethical concerns for some consumers. Additionally, the availability of mammalian stomachs for rennet production is limited, impacting the production of pepsin-containing rennet.
To address these concerns, cheese producers have explored alternative sources of enzymes, such as microbial, plant, and fungal sources. These substitutes are suitable for vegetarians and those keeping Kosher or Halal diets. However, some of these coagulants may lead to bitter and undesirable flavours, especially in cow's milk cheeses. As a result, cheesemakers must carefully select the appropriate rennet type and aging process to balance flavour, texture, and ethical considerations.
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Lipase: found in animal or microbial sources
Lipase is an enzyme that is commonly found in rennet, a complex set of enzymes produced in the stomachs of ruminant mammals. While rennet is traditionally sourced from animals, specifically calves, kid goats, and cows, it can also be derived from microbial sources.
The use of animal rennet in cheese production has been declining, with less than 5% of cheese in the United States made using this method today. This is partly due to the limited availability of mammalian stomachs and the desire to find suitable alternatives for vegetarians and those keeping kosher or halal diets.
Lipase from animal sources is a component of traditional rennet, which contains other enzymes such as chymosin and pepsin. Calf rennet, in particular, contains these enzymes in a natural ratio that contributes to a desirable flavour profile and more reliable results in yield. However, the use of animal-sourced rennet has sparked debates about ethical and dietary concerns, with some consumers seeking transparency in ingredient labelling.
Lipase from microbial sources offers an alternative to animal-based rennet. Microbial rennet is commonly used in the production of kosher cheeses and has improved over time due to the characterization and purification of secondary enzymes. This improvement has resulted in the creation of several high-quality cheeses with a reduced presence of bitter peptides, making it a versatile option for cheese makers.
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Fermentation-produced chymosin: used in industrial cheesemaking
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. It has traditionally been used to separate milk into solid curds and liquid whey for cheesemaking. Chymosin, the key component of rennet, is a protease enzyme that curdles the casein in milk, causing coagulation.
As the availability of rennet from animal sources is limited, cheesemakers have sought alternative methods to coagulate milk. Fermentation-produced chymosin (FPC) is a commonly used alternative, created through microbial fermentation. This process involves isolating rennet genes from animals and introducing them into bacteria, fungi, or yeast cultures, which then produce recombinant chymosin. The genetically modified microorganism is then removed, and the chymosin is isolated from the fermentation broth. This ensures that the final product, FPC, does not contain any genetically modified organisms.
FPC is widely used in industrial cheesemaking in North America and Europe due to its cost-effectiveness and suitability for large-scale production. As of 2008, 80-90% of cheeses in the United States and Britain were estimated to utilize FPC. However, FPC has been banned in several countries that prohibit the genetic engineering of food products.
The use of FPC in cheesemaking is a topic of debate, with ongoing discussions regarding its status as a genetically modified organism. While some consider it safe and reliable, others have concerns about the potential impact on the health of the food system. Nonetheless, FPC plays a significant role in the modern cheesemaking industry, allowing for efficient and sustainable cheese production.
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Frequently asked questions
Rennet is a complex set of enzymes produced in the stomachs of ruminant mammals. It is used to separate milk into solid curds and liquid whey, which is used in cheesemaking.
The key enzyme in rennet is chymosin, which curdles the casein in milk. Rennet also contains enzymes like pepsin and lipase.
Some non-animal sources of enzymes include plants, fungi, and microbial sources. Specific examples include thistle, Cynara (artichokes and cardoons), and Rhizomucor miehei, a type of mold.
Non-animal enzymes are used in cheesemaking to cater to vegetarian, vegan, kosher, and halal diets. They are also more cost-effective than animal rennet.
Yes, there are different types of rennet, including traditional calf rennet, vegetable rennet, and microbial rennet. The type of rennet used can impact the flavor profile and yield of the cheese.
